It is known that a multiplicity of different color shades is used in industrial paint lines, for example in paint lines for automobile bodies or attachments. Paint lines of this kind can be robot-based, and with cycle times of 60 s to 90 s, for example, can be designed to paint a different color shade in each cycle, 20 to 60 different color shades can be a common number in the automobile industry. Color changers can be provided in order, for example, to supply an atomizer mounted on a robot arm with a paint material of a specified color shade. These have a multiplicity of inlets for paint material which are connected to appropriate supply lines for the different paint materials. As a rule, the paint materials are made available at different take-off points along the paint line by means of so-called ring mains, and from there are fed to the respective color changer by means of the supply lines. A color changer also has a common manifold channel, into which the supply lines open out at least indirectly, its outlet being connected by means of a line to the atomizer which is to be supplied with paint material.
Valve means are provided between the respective inlets of the color changer and the common manifold channel. Depending on which of the valve means is open, the appropriate paint material is fed into the manifold channel during painting and from there routed to the atomiser. At least one inlet of a color changer is usually connected via a valve means to a solvent line in order, in the event of a color change, to clean the manifold channel for the next paint material with a different color shade. A supply of an air-solvent mixture, which is produced by an alternating pulsed supply of air and solvent, is also frequently used when cleaning. The cleaning effect of such a mixture is considerably increased while the solvent consumption is reduced.
The strict separation of different color shades is of great importance, as even the smallest color residues can lead to an alteration of the color shade, for example in the case of a marginal residue of a red color shade in a white color shade. Valve means are subject to wear, and leakages can therefore also occur in the course of time. When a valve means no longer closes reliably, then, in spite of an actually closed state of a valve means, marginal quantities of a paint material of a first color shade can find their way into the manifold channel and mix with a paint material of a different color shade located therein.
Leakage faults of this kind cannot be seen from outside a color changer. They are therefore usually only discovered very late, namely for example on a significantly defectively painted body. Depending on the combination of the successive color shades, faults of this kind may also only be discovered after several days on the basis of a defectively painted body. The damage resulting from defectively painted bodies is considerable, as these have to be completely refurbished and repainted. As, in a paint line, a multiplicity of paint robots are involved sequentially in painting one and the same object, the association of defective painting with a respective paint robot or the color changer belonging thereto usually proves to be very difficult or impossible. When a paint changer is defective, a paint line therefore usually has to be shut down for the duration of fault finding, as a result of which its production capacity is reduced in a disadvantageous manner.